At 12:03 PM -0700 4/8/07, Sean Kamath wrote:
[...]
It's not just dovecot, by the way. MANY things don't like have time move backward, like Cron, at, etc.
Absolutely.
You should *NEVER* have the clock jump back in time (except during DST changes -- yuk).
DST changes (at least on sane systems) do not change the system clock time. Time zones are a cosmetic feature, i.e. how humans are shown a description of time. For example, the following are different ways of displaying exactly the same time:
12:03 PM -0700 4/8/07 15:03 PM EDT 4/8/07 14:03 PM EST 4/8/07 19:03 PM -0000 4/8/07 00:03 PM +0500 4/9/07
The correct way to handle time on Unix systems is to set the clock at boot (rdate, ntpdate, etc), and then *skew* the clock, so time slows down to match the right time. It can always jump forward, but NTP only jumps by a (settable) maximum amount per time-quantum. This prevents things like make, and NFS caching, and a bunch of other stuff "just work".
As far as I know, all shipping OSes now have a working NTP client, and it's VERY easy to just add
server pool.ntp.org
to the ntpd.conf file, and you're good to go on reboot.
It is important for people to understand how much simpler it is now to run basically functional and non-abusive NTP than it was even 5 years ago. The work put into making pool.ntp.org usable has essentially eliminated the need to think much about NTP for most sites.
--
Bill Cole
bill@scconsult.com